Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$239.86	6.391%	$255.1895	$255.19	$255.20	$255.20
Purchase #2	$237.99	4.725%	$249.235	$249.24	$249.25	$249.20
Purchase #3	$96.41	7.554%	$103.6928	$103.69	$103.70	$103.70
Purchase #4	$85.77	6.826%	$91.6247	$91.62	$91.60	$91.60
Purchase #5	$99.54	10.112%	$109.6055	$109.61	$109.60	$109.60
Purchase #6	$140.77	7.648%	$151.5361	$151.54	$151.55	$151.50
Purchase #7	$84.66	7.503%	$91.012	$91.01	$91.00	$91.00
7 purchase totals =	$985.00		$1,051.8956	$1,051.90	$1,051.90	$1,051.80